This invention relates to a liquid crystal display unit and, more particularly, to a an in-plane switching type liquid crystal display unit and a process for fabricating the in-plane switching type liquid crystal display unit.
An active matrix liquid crystal display unit has an image producing plane, which is implemented by a matrix of pixels. The pixels are respectively associated with thin film transistors, and the pixel electrodes are selectively connected to data lines through the associated thin film transistors. Image carrying signals are supplied to the selected pixel electrodes, and change the transparency of the liquid crystal at the selected pixels by changing the electric field between the selected pixel electrodes and the common electrode. Thus, the transparency of liquid crystal is precisely controlled, and a high-quality image is produced on the matrix of the pixels.
The transparency of liquid crystal is varied by changing the directors of the liquid crystal molecules. When the liquid crystal display unit has the twisted nematic liquid crystal, the directors of the liquid crystal molecules are rotated toward a direction normal to the image producing surface. On the other hand, if the directors of the liquid crystal molecules is twisted to a direction parallel to the image producing surface, the liquid crystal display unit is categorized in the in-plane switching type.
The in-plane switching type liquid crystal display unit has two substrate structures, and the liquid crystal is confined between the two substrate structures. The thin film transistors are fabricated on the first transparent substrate, and the pixel electrodes and the common electrodes are further formed on the first transparent substrate. The pixel electrodes have a comb-like shape, and the common electrodes also have a comb-like shape. The pixel electrodes and the common electrodes are arranged on the first transparent substrate such that the common electrodes are interdigitated with the pixel electrodes. Potential difference is applied between the pixel electrodes and the common electrodes, and creates electric fields between the pixel electrodes and the common electrodes in parallel to the first transparent substrate. The electric fields give rise to change of the directors of the liquid crystal molecules, and the transparency is varied. The directors are rotated on the planes parallel to the first transparent substrate. The in-plane switching type liquid crystal display unit is more attractive than the twisted nematic type liquid crystal display unit, because the relation between the amount of transmitted light and the applied potential difference is not widely varied in the range from the direction of the directors and the normal line to the first transparent substrate. For this reason, the in-plane switching type liquid crystal display unit produces fine images in the wide angle of view.
The liquid crystal in the in-plane switching type liquid crystal display unit has a homozygous orientation. The liquid crystal is sandwiched between two polarizing plates. The polarizing plates have respective planes of polarization which are perpendicular to each other. One of the polarizing plates has the direction in parallel to the orientation. When the potential difference is removed from between the pixel electrodes and the common electrodes, the light is interrupted by the liquid crystal, and the image producing surface becomes black. The luminance is low and stable. A potential difference is applied between a pixel electrode and the associated common electrode. The liquid crystal molecules are rotated in the direction of the electric field, and permit the light to pass therethrough. For this reason, the pixel becomes white.
FIGS. 1 and 2 show a prior art liquid crystal display unit. The prior art liquid crystal display unit is broken down into a lower substrate structure, an upper substrate structure and liquid crystal confined between the lower substrate structure and the upper substrate structure. Thin film transistors are incorporated in the lower substrate structure, and color filters are formed in the upper substrate structure.
The lower substrate structure is fabricated on the basis of a transparent substrate 1. Gate electrodes 2 and a common electrode 3 are formed on the transparent substrate 1, and are covered with an inter-layered insulating layer 4. Data lines 6 and a pixel electrode 7 are patterned on the inter-layered insulating layer 4, and are covered with a passivation layer 8. The gate electrodes 2 extend perpendicular to the data lines 6, and thin film transistors 5 are assigned to regions where the gate electrodes 2 cross the data lines 6. The pixel electrode 7 is offset from the common electrode 3, and is in parallel to the common electrode 3. An orientation layer 18 is formed on the passivation layer 8, and a polarizing plate 16a is attached to the lower surface of the transparent substrate 1. The data lines 6 and the pixel electrode 7 are hatched in FIG. 1 for discriminating them from other electrodes.
On the other hand, the upper substrate structure has a transparent substrate 11, and a black matrix 12 and colored layer 13 are formed on the lower surface of the transparent substrate 11. The colored layers 13 serve as color filters. The black matrix 12 and the colored layers 13 are covered with a flattening layer 14, and an orientation layer 18 is formed on the lower surface of the flattening layer 14. The upper surface of the transparent substrate 11 is covered with a conductive layer 15, and a polarizing plate 16b is attached to the upper surface of the conductive layer 15.
The upper substrate structure is spaced from the lower substrate structure in such a manner that the orientation layers 18 are opposed to each other, and the liquid crystal 17 fills the gap between the orientation layers 18. The orientation layers 18 was subjected to a rubbing at a certain angle with respect to the longitudinal direction of the pixel electrode 7, and the liquid crystal 17 has homogenous orientation in a direction indicated by arrow A1.
The polarizing plate 16a has a plane of polarization which is perpendicular to a plane of polarization of the other polarization plate 16b. One of the planes of polarization is in parallel to the orientation of the liquid crystal molecules 17. The pixel electrode 7, the color filter 13 and part of the liquid crystal 17 therebetween form a part of the pixel. The transparency of the part of the liquid crystal over the pixel electrode 7 is changed as follows. First, the gate electrode 2 is changed to the active level, and the associated data line 6 is driven to a certain potential level. The thin film transistor 5 turns on, and the certain potential level reaches the pixel electrode 7. A lateral electric field is created between the pixel electrode 7 and the common electrode 3, and the liquid crystal molecules 17 are rotated in the planes parallel to the lower substrate structure. As a result, the transparency of the liquid crystal over the pixel electrode 7 is changed.
A problem is encountered in the prior art in-plane switching type liquid crystal display unit in that the pixels do not promptly respond to the potential level applied to the associated pixel electrodes 7. Another problem is unintentionally colored pixels on the image producing surface.
It is therefore an important object of the present invention to provide a liquid crystal display unit, which is promptly responsive to image-carrying signals for producing a picture without any unintentionally colored pixel.
It is also an important object of the present invention to provide a process for fabricating the liquid crystal display unit.
In accordance with one aspect of the present invention, there is provided an in-plane switching type liquid crystal display panel for producing images comprising a pair of substrate structures opposed to each other for creating a gap therebetween, and liquid crystal filling the gap, and serving as optical elements of plural pixels where the images are produced, each of the plural pixels includes a common electrode formed in one of the substrate structures of the pair, a pixel electrode formed in the aforesaid one of the substrate structures in an offset manner to the common electrode, and defining a zone in the liquid crystal together with the common electrode for accommodating one of the optical elements of the plural pixels therein and a switching transistor formed in the aforesaid one of the substrate structures and having a source connected to the pixel electrode, a data line extending outside of a periphery of the zone and a gate electrode extending outside of the periphery, and the in-plane switching type liquid crystal display unit further comprises at least one partition wall structure associated with the aforesaid each of the plural pixels, formed in any one of the substrate structures and projecting into the zone for separating at least part of the aforesaid one of the optical elements from the remaining liquid crystal.
In accordance with another aspect of the present invention, there is provided a process for fabricating an in-plane switching type liquid crystal display unit comprising the steps of a) preparing substrate structures one of which includes at least one partition wall structure occupying an area partially overlapped with a pixel electrode forming a part of one of plural pixels and a common electrode associated with the pixel electrode, a switching transistor connected with the pixel electrode, a data line connected to the switching transistor being located out of the area, b) assembling the substrate structures in such a manner as to form a gap therebetween and c) introducing liquid crystal into the gap so that part of the liquid crystal fills a zone defined by a periphery of the at least one partition wall structure.